Starch is a naturally occurring carbohydrate present in different parts of the plant like in the stem, roots, seeds, fruits, etc. Starch appears as an odourless, tasteless, fine powder. Starch consists of two components amylose and amylopectin. Amylose is present in the form of linear chains and amylopectin is present in the form of a branched-chain polymer.
Starch consists of 20-30% Amylose and 70-80% of amylopectin. Both amylose and amylopectin are present in crystalline and granular forms. Amylopectin is present as a crystalline structure. Amylose because of its linear structure is insoluble and amylopectin because of its branched structure form jelling and viscus preparations.
Moisture Content
Starches are hygroscopic and take moisture from the surrounding environment.
when stored at 50% RH following moisture level is present in different types of starches.
- 12%Corn Starch
- 13%Wheat Starch
- 14%Rice starch
- 18%Potato Starch
Use in Pharmaceutical industry
Starch is widely used in pharmaceutical industries, usually in the manufacturing of tablets, capsules and other solid dosage forms. Major functional category of starch is as
- Tablet and capsule Binder
- 3-20 %(usually 5-10%)
- Tablet and capsule Disintegrant
- 3-25%(usually 15%)
- Tablet and capsule Diluent
Other Uses Of Starch
- Antiadherent and lubricant (3-10%)
- Topical preparations
- Plasma volume expanders
- Treatment of Diarrhea
Starch as Binder
Binders are used in wet granulation for converting powders into granules. Binder prevents capping and lamination of the tablet. Disintegration and dissolution profile of tablets and capsules is greatly affected by binder type and quantity. Starch is commonly used as a binder in tablet and capsules manufacturing. Starch in the concentration of 3-20 %(usually 5-10% basis on the starch type) is used as a binder. Native starch is insoluble in cold water so to use it as a binder starch paste is prepared. Freshly prepared starch paste is used as a binder because starch is susceptible to microbial growth. To prepare a starch paste, the starch suspension is prepared in cold water and then it is heated. On heat, the gel-like structure starts forming and after a few minutes, a viscous paste is formed. This starch paste is used as a binder in tablet and capsule manufacturing by wet granulation.
Important Topic
Wet granulation method of tablet manufacturing.
Starch as Disintegrant
Disintegrants are the agents which break tablets into small parts and release Active pharmaceutical ingredients or API. Starch Is commonly used as a disintegrant in tablets and capsules. The first excipient used as a disintegrant in tablet manufacturing was native starch. Native Starch acts as a disintegrant and disintegration mechanism is by Wiking e.g take up water by capillary action.
Starch is used as disintegrant both as extra granular and intra-granular. Usually, half the quantity is added as intra-granular and half is added extra granular or depending on the formulation. Starch is a fine powder and its compressibility is low so when large quantities are used in the extra-granular form it results in capping and lamination so try to use most of the quantity of starch as intra-granular.
Starch in concentration 3-25%(usually 15%) is used as disintegrant.
Starch as Diluent
Diluents are used to increase the bulk volume of the tablets or capsules. Starches are commonly used diluents used in pharmaceutical industries for the manufacturing of tablets and capsules. These are used for potent drugs, to prepare colour mixtures and also used in herbal products.
Starch as Glidant
Dry starch is also used as a glidant and enhances the flow properties.
Anti-adherent And lubricant
Starch prevents sticking so it is used as a lubricant and anti-adherent. Starch in concentration 3-10% is used as anti-adherent and lubricant in capsule preparations.
Starch in Topical Preparations
Wheat and rice starch are also used as adsorbent of fluids in a topical preparation. Starch is also used in ointments.
Plasma volume
Starch is also used in plasma volume expander preparations.
Modified Starches
Native starch is modified by a physical method like pregelatinized or by chemical method e.g cross-linking method to change its physical and chemical properties.
Pregelatinized Starch
Pregelatinized starch occurs as coarse to a fine powder and is soluble in cold water.
Pregelatinized starch is prepared by cooking the native starch and then drying it and milling it to form a modified starch which is soluble in cold water.
Pregelatinized starch has better compressibility, better flow and better disintegration properties.
There are two grades of pregelatinized starch
- Partially pregelatinized Starch
- Fully pregelatinized Starch
Partially Pregelatinized Starch
Usually, this starch contain
- 5% Amylose
- 15% amylopectin
- 80% unmodified starch
it increases flow properties and is used in direct compression.
Fully Pregelatinized Starch
It contains
- 20% Amylose
- 80% Amylopectin
It gives cold water solubility properties so it is used as a binder in wet granulation for the manufacturing of tablets and capsules.
Synonyms of pregelatinized starch
- Compressible Starch
- Starch 1500 G
- Merigel
- Prejel
Uses of Pregelatinized Starch
Pregelatinized starch is used as
- Diluent (Hard gelatin capsule) (5-75%)
- Tablet Binder for direct compression (5-20%)
- Tablet Binder for wet granulation (5-10%)
- Tablet Disintegrant (5-10%)
Sterilizable Maize Starch
It is modified starch and is used as lubricant and diluent. It is used as a lubricant for surgical gloves and also used in dusting powders.
Sodium Starch Glycolate
Sodium starch glycolate is a modified starch prepared by cross-linking modification of potato starch.
Sodium starch glycolate has 3 types,
- Type A
- Type B
- Type C
These types differ in pH and contents of sodium and sodium chloride.
Uses of Sodium Starch glycolate
Sodium starch glycolate is used as
- Tablet Disintegrant 2-8%
- Capsule Disintegrant 2-8%
Usually, the optimum concentration is 4%.
Sodium starch glycolate is effective even in very low quantities at 2%.
As compared to native starches which are used in higher quantities to give disintegrating properties, modified starches give better disintegration effects even in low concentration.
Synonyms of sodium starch glycolate
- Tablo
- Sodium salt
- Carboxymethyl starch
Swelling Properties
Sodium starch glycolate swells up to 300 times its original size when coming in contact with water.
Note:
- Tablets prepared by sodium starch glycolate are more stable.
- Sodium starch glycolate is incompatible with ascorbic acid.
- Sodium starch glycolate causes irritations to eyes so proper protective measures should be taken during its use.
- Should be stored in a well-closed container.